Bori Shushan

LC/MS and LC/MS/MS Screening for the Sites of Post-Translational Modification in Proteins

Coupled high performance liquid chromatography/mass spectrometry (LC/MS) is utilized for the molecular weight determination of peptides from enzymatic digests of proteins. Methods designed to identify the individual peptides that contain sites of phosphorylation are described and demonstrated for the Lys C digest of the nicotinic acetylcholine receptor (AChR). The technique employs both the use of LC/MS and coupled LC/tandem mass spectrometry (LC/MS/MS) to screen for the neutral loss of phosphate from the peptides. The coupling of HPLC and mass spectrometry is accomplished through the use of an atmospheric pressure ionization source (API) and IonSpra® LC/MS interface on a triple quadrupole mass spectrometer.

Modulated-field linked-scan studies of metastable ions

Abstract Appropriate linked scans (B/E or E2/V) of two of the three fields of a double-focussing mass spectrometer provide fragment-ion spectra of preselected parent ions, with effective mass resolution of the fragment-ion peaks which is considerably higher than that obtainable in other methods of obtaining spectra of metastable ions. However, the diagnostic capability of these scans is limited by artifact peaks of various kinds, which can arise from fragmentations of parent ions with m/z values close to that actually selected. It is shown how AC modulation of V or of E, with appropriate phase-sensitive detection, can identify the artifacts, and in suitable cases reduce their intensity almost to zero. Experimental examples illustrate both the power and the limitations of the technique.

Derivation of scan laws for detection of consecutive ion fragmentations in conventional double-focussing mass spectrometers

Abstract The theory of linked scans of the three fields of a conventional double-focussing mass spectrometer, which permit detection of consecutive fragmentations in the first two field-free regions, is presented. It is possible to select the masses of any two of the five species involved, and thence deduce linked-scan laws which will, in principle, completely define the reaction sequence. The potential uses of such linked scans in mixture analysis are particularly stressed. As in linked scans for single-step fragmentations, artifact peaks of various kinds must be considered.

Further experiments concerning an ambiguous assigment of a metastable peak to a sequential fragmentation process in 3-chlorophenol

Abstract Ambiguities in assigning metastable peaks observed in conventional double-focussing instruments, to consecutive fragmentations of ions (one reaction in the first field-free region, the other in the second), have been re-examined for the case of 3-chlorophenol. By varying the ionising electron energy, it was possible to eliminate interference from artifacts due to fragmentations of doubly-charged molecular ions within the electric sector. The effect of collision gas was also examined, and found to increase the sensitivity by a factor of about two, but to also increase the relative importance of the artifacts.

Materials Characterization Using Thermogravimetry Coupled to Triple Quadrupole Tandem Mass Spectrometry (MS/MS)

Thermogravimetric analysis (TGA) coupled with sequential mass spectrometry (MS/MS) offers unambiguous structural identification of compounds evolving during thermo-degradative processes without interrupting the TGA-mass spectrometer analytical procedure. MS/MS identification of co-evolving compounds, combined with the weight-loss data obtained from TGA, furnishes a means of delineating complex thermolytic pathways. The compatibility of TGA (an atmospheric pressure technique) with Atmospheric Pressure Chemical Ionization (APCI), as offered on the TAGA® 6000 MS/MS system, permits an interface which is easily coupled and decoupled making the system “user-friendly” and well suited to routine quality control and trouble-shooting applications.